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Excision of a Schwannoma from the proximal radial nerve, using posterior approach to proximal humerus

    Overview

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    Learn the Excision of a Schwannoma from the proximal radial nerve, using posterior approach to proximal humerus surgical technique with step by step instructions on OrthOracle. Our e-learning platform contains high resolution images and a certified CME of the Excision of a Schwannoma from the proximal radial nerve, using posterior approach to proximal humerus surgical procedure.
    Schwannomas are benign peripheral nerve sheath tumours. They are rare, but the true incidence is unknown because they frequently present as incidental findings on magnetic resonance imaging (MRI). When superficially located they may present as painful lumps with electrical sensory symptoms of pins and needles, tingling and pain when knocked. When they occur in deeply located nerves they may present with symptoms associated with nerve compression especially if the tumour is sited at anatomically tight space.
    Schwannomas grow slowly and the nerve accommodates the growing tumour, with neurological symptoms developing when compression is critical or the tumour reaches a size that distorts and compresses otherwise normal fascicles within a peripheral nerve. The symptoms experienced are dependent on the type of nerve and its anatomical location. Most tumours fall into the benign category and are either Schwannoma or Neurofibroma subtypes. Most are solitary but both can present as multiple tumours in neurofibromatosis. Multiple Schwannomas are also a feature of the separate genetic condition Schwannomatosis in which strings of multiple tumours may arise from a single nerve trunk.
    Excision is recommended when they cause neuropathic pain or when there is developing neurological deficit. Following excision superficial nerves may remain sensitive or tethered in scar tissue. There is also a small risk of permanent neurological deficit following excision. The risk is greater after previous biopsy, in large tumours and with recurrent tumours. The decision to operate is usually based on symptom profile, careful clinical examination and MRI features. Atypical tumours with indeterminate imaging should be referred to a specialist unit where there is a soft tissue sarcoma MDT and biopsy planned with review of histopathology prior to excision. Malignant nerve sheath tumours are extremely rare but require specialist management for excision and reconstruction where indicated. The margins for excision are greater for proven or suspected malignant tumours and the focus in such cases is on tumour clearance rather than functional preservation, the opposite objective to that for benign tumours.
    The case presented is a large Schwannoma in the radial nerve as it leaves the posterior axilla and extends into the spiral groove. The tumour was removed using a posterior approach to the humerus because of increasing size, pain, sensory symptoms and motor weakness. Prior to surgery the tumour had a biopsy and following this there was more pain, an increased tumour size and transient complete motor loss. Repeated imaging with MRI after the biopsy demonstrated a fluid level and suspected vascular malformation within the tumour.


    Indications

    Indications:
    Nerve tumours are rare and most are asymptomatic. Surgery is indicated for cases with established motor and sensory abnormalities, superficial tumours susceptible to local repeated trauma and where there is diagnostic uncertainty.
    Each patient must be counselled specifically for their particular tumour by virtue of its location and size and nature. Non-critical sensory nerve tumours may be removed with less morbidity than a proximal tumour in a mixed motor and sensory nerve. The patient must be aware of the risk of neurological deterioration following surgery. This at minimum may be transient secondary to oedema but there is a risk of creating an axonotmesis type injury from intraneural dissection as well as the possibly need for resection of an involved fascicle group for tumour clearance.
    Symptoms and examination:
    Benign peripheral nerve sheath tumours may be asymptomatic but often present with painful lumps that are prone to local minor trauma, particularly when situated in superficial sensory nerves. Schwannomas in main mixed motor and sensory nerve trunks are usually deeply sited and may remain asymptomatic unless they occur at anatomically tight spaces or if they increase in size and cause compression and distortion of normal fascicles within the nerve. In this latter case they will result in progressive sensory and motor dysfunction dependent on the nerve affected and the location. A careful examination should determine any deficit using the Medical Research Council (MRC) grading system and quantitative sensory testing with monofilaments and moving and static two-point discrimination.
    Tinel’s sign is the sensation of parasthesiae or dysesthesiae on gently tapping on the nerve eat the site of the tumour. The sensory symptoms are perceived in the cutaneous territory of the nerve. Motor nerves often present with deep ache on tapping and the sclerotome innervation pattern is normal.I would recommend that the Tinel’s sign is left until the end of the examination because unpleasant sensory symptoms can persist and compromise the other examination tests. The Tinel’s sign should commence distally on the nerve and proceed proximally to the site of suspected nerve sheath tumour. Synchronous and occult tumours may be detected using this systematic approach.
    In this case there was a mass in the region of the triangular space and spiral groove with sensory reduction and pina=s and needles in the posterior cutaneous nerve of arm and superficial radial nerve territories. There was mild motor dysfunction with wasting of the brachioradialis and the radial wrist extensors. Finger extension was MRC grade 4. The palpable mass was firm, deep to the deep fascia and triceps and did not transilluminate. It could not be moved in a longitudinal plane but was readily mobile in a sideways direction, suggestive that is was situated in a longitudinal structure. There was a string Tinel’s sign radiating to the posterior cutaneous nerve of the arm and the superficial radial nerve territories.
    Investigations:
    Imaging of suspected nerve sheath tumours with MRI +/- ultrasound is mandatory prior to consideration of surgical removal.
    Ultrasound is a useful investigation that allows rapid screening of the more superficially-placed nerves in the limbs. As a dynamic investigation, tether points and areas of compression may be visualised. The investigation is operator dependent and the images are difficult to interpret and offer little guidance on the site of epineural window placement.
    MRI is superior in looking at the nerve architecture and MR neurography is a developing field that can provide useful information on fascicular arrangements around the tumour and can therefore assist in planning tumour excision.
    If there are any unusual features on imaging or worrying clinical presentation (nerve pain, rapidly increasing in size, recurrence at a site of previous resection, major motor or sensory dysfunction) then consideration should be given to a nerve biopsy prior to planning definitive surgical management.
    In uncertain cases the use of MRI spectroscopy shows promise in identifying abnormal proteins (trimethylamine that may be associated with atypia or malignancy). Perhaps in the future these types of chemical imaging plus functional imaging (PET scanning) may provide diagnostic information sufficiently accurate to negate the need open nerve biopsy.
    Neurophysiology assessment with electromyography may demonstrate denervation changes that can confirm the extent of neurological compromise prior to any surgery and can assist in counselling patients on excision and the attendant risks prior to surgery.
    Non-operative management:
    Small asymptomatic tumours with no adverse features on clinical examination or imaging may be clinically monitored with repeat imaging only if there is a change in size or symptom profile. Tumours can be observed when there are minimal symptoms, no neuropathic pain and no sensory or motor disturbance as long as imaging is typical for a benign peripheral nerve sheath tumour.
    Simple decompression of nerves containing tumours at tight anatomical points such as the cubital tunnel, pronator arch and carpal tunnel is a strategy when there are multiple symptomatic tumours.
    Alternative operative management:
    For benign tumours simple excision biopsy should suffice but the operation should be performed with great care to prevent further loss of nerve function. If there is diagnostic uncertainty and imaging is inconclusive consideration should be given to a formal open incisional biopsy of the lesion. The biopsy should include the interface with normal nerve tissue and so results in damage and scar that makes it more likely that there will be permanent neurological dysfunction after tumour resection.
    In simple cases with routine imaging and clinical findings we recommend a marginal excision of the tumour by way of excision biopsy to prevent these problems. It must be noted that despite these precautions there are still cases of inadvertent marginal excision of malignant tumours although these tend not to be neurofibrosarcomas but usually atypical presentions of tumours such as synovial sarcoma or intra-neural Ewing’s sarcoma. Therefore, it is essential that all potential surgical cases are discussed in a multidisciplinary meeting with review of imaging, clinical presentation and any previous histology or biopsy findings. The appropriate surgical procedure can then be planned. For malignant tumour resection wide margins are required with radical excision of surrounding normal tissue to ensure that the tumour is not breached. Reconstruction of the nerve in these rare cases must be planned and depends on the adjuvant therapy planned and the site of the nerve gap. Options include nerve grafting, nerve allografting, distal nerve transfers and tendon transfers.
    In this case simple excision was recommended based on the clinical findings, imaging and the chronic history.
    Contraindications:
    Surgery should not be undertaken outside of a specialist unit if there is a suspicion on imaging of malignant peripheral nerve sheath tumour. In such cases definitive management should be done by a sarcoma specialist and should involve radical excision margins with compartment excision or amputation. Surgical marginal excision biopsy should not be performed without counselling the patient regarding the small risk of permanent sensory loss, motor weakness or paralysis and neuropathic pain in the effected nerve territory.

    Setup

    Set up:
    The patient had general anaesthesia without neuromuscular blockade to allow intra-operative nerve stimulation.
    Nerve stimulation may be used to define the fascicle anatomy and identify any important branches as the tumour is exposed. When the tumour is removed any fascicles entering the tumour can also be assessed to establish the potential for functional loss and provide a prognosis. Residual function can also be mapped in the preserved nerve.
    The limb is prepped and draped from the neck leaving the affected hand fully exposed so that the motor function may be assessed accurately with nerve stimulation intra-operatively as required. Due to the tumour location no tourniquet was used and monopolar diathermy and bipolar cautery are both available. Near the nerve the bipolar is used to prevent electrical current dissipating along the nerve. An electrode is placed close to the surgical field to complete the nerve stimulator circuit.
    The patient is positioned in the lateral position with the affected arm uppermost and supported in a gutter. Thromboembolic deterrent stockings are applied to the lower limbs and pneumatic pressure socks to reduce the risk of venous thromboembolism. More distally sited tumours may be removed under regional anaesthesia as long as no local anaesthetic is injected at the site of surgery prior to tumour removal. Proximal regional blockade produces a segmental conduction block and distal stimulation and motor assessment is still possible. In cases of planned nerve excision, one or both lower limbs will need preparing if autologous sural nerve cabled grafting is planned to reconstruct a nerve gap. This is not planned in this case where an excision biopsy is planned preserving the intact fascicles in the radial nerve.
    Basic hand instruments are required for the superficial exposure, surgical rubber sloops may be used for identification of the nerve, delivery to the wound and gentle retraction. Microsurgical instruments including jeweller’s forceps and curved serrated nerve scissors are ideal for the intraneural dissection. An operating microscope is needed for the intraneural dissection. A nerve stimulator is required. I prefer to use a regional anaesthetic stimulator needle within an arthroscopy camera drape and connected to the anaesthetic nerve stimulator box. In this way an unscrubbed member of the team is able to control the stimulator settings and adjust as needed to measure nerve function at the request of the operating surgeon.

    Operation – 1

    The patient is positioned in the lateral position with posts supporting the pelvis and a gutter support under the right humerus. Soft wool-gauze padding is placed in the axilla to prevent compression of the infra-clavicular plexus against the edge of the gutter support.
    The anatomy at the posterior shoulder pertinent to dissection around the triangular space has been marked on the skin with a permanent marker prior to skin preparation.
    The triangular space, inferior to the teres major tendon(1), lateral to the long head of triceps(2) and medial to the humeral shaft, is marked.
    The radial nerve passes posteriorly through this space to leave the axilla and enter the spiral groove deep to triceps.

    The view from the anterior aspect demonstrates that the arm to be operated hangs free. It will be prepped to allow visualisation of the muscle responses during nerve stimulation intra-operatively.

    The uppermost ipsilateral leg is marked and prepared in case of need for sural nerve harvest. The lower leg has a compression stocking and a pneumatic pressure sock to reduce venous thromboembolism risk.
    Nerve grafting may be required when there is a need to resect fascicles from the nerve during tumour excision.

    The course of the sural nerve is marked.
    This lies on a line between the mid-point of the gastrocnemius at the lower aspect of the popliteal fossa to a point at the ankle mid-way between the posterior aspect of the lateral malleolus and the achilles tendon.

    The patient is positioned in the lateral position with the right side uppermost. The upper arm is supported in a short gutter support with padding to the axilla.The whole limb is prepped and drapes are placed above the shoulder.
    The triangular space, inferior to the teres major tendon, lateral to the long head of triceps and medial to the humeral shaft, is marked.
    The radial nerve passes posteriorly through this space to leave the axilla and enter the spiral groove deep to triceps. The nerve is accompanied by the profound brachii artery here.

    The triangular space, inferior to the teres major tendon, lateral to the long head of triceps and medial to the humeral shaft, is marked.The site of the tumour is palpable and marked with the circle. The longitudinal line marks the course of the radial nerve and the site of the surgical incision.
    The photograph is taken from the anterior aspect of the patient.

    The skin incision is marked and incised along the line of the radial nerve which passes posteriorly through the triangular space to leave the axilla and enter the spiral groove deep to triceps.The orientation has now been changed and the photograph is taken from the posterior aspect of the patient where the surgeon is standing.
    The skin is incised alone the course of the radial nerve.

    Bipolar diathermy is used to coagulate small vessels under the dermis.

    Monopolar diathermy may be used for the superficial dissection, but should not be used in the deep dissection close to the nerve due to the risk of electrical conduction along the nerve and iatrogenic damage.

    Dissection continues down to the deep fascia which is defined then incised.The white triceps tendon and its epimysium is now seen in the upper part of the dissection.

    The Triceps is defined in particular to identify its long and lateral heads.The photograph recording orientation is changed and now the image is taken from the anterior aspect. The shoulder is at the top of the images and the proximal skin markings can be seen. the triangular space lies below the teres major (1)
    The skin is incised and monopolar diathermy can be used for haemostasis and dissection to the deep fascia. The fascia is opened and the nerve tumour can be palpated deep to the triceps tendon and muscle. The interval between the long and lateral heads of the triceps in the posterior upper arm will be opened to allow access to the triangular space and the radial nerve in the spiral groove.
    Self-retaining retractors are placed to assist with exposure of the tumour.

    The triceps interval is developedThe interval in the triceps between the long and lateral heads is identified and this plane developed carefully with the Jamieson scissors.

    The Langenbeck retractor(1) assists retracting the long head of triceps to identify the inter-triceps interval to reach the radial nerve.

    The fascia between the two upper triceps heads is split.The long head is seen being mobilised here, with release of the proximal fascia.
    The broad Langenbeck retractor is being used to demonstrate the inter-triceps interval in the upper part of the incision. The radial nerve lies in this fat layer.

    The radial nerve is carefully exposed lyiing deep to the separated triceps headsThe lateral head of triceps has been mobilised and the two self-retaining retractors have been repositioned to allow exploration of the inter-triceps interval.

    A Mixter forceps is placed under the radial nerve distal to the tumourA mixter forceps is passed deep to the radial nerve, distal to the palpable tumour. The mixter has jaws at 90 degrees to the shaft and this facilitates their passage without excessive handling of the nerve.

    A blue sloop is passed deep and distal to the radial nerve and the nerve can now be gently retracted with minimal handling which facilitates controlled dissection of the nerve.The bulging tumour can be seen proximal to the sloop. Care should be taken when dissection proceeds retrograde along a nerve in case the dissection enters the “axilla” of a branch point and inadvertent iatrogenous injury to a branch follows. This is less of a risk than in a scarred nerve, however the operating surgeon should be cautious due to the potentially distorted anatomy.
    At the apex of the tumour, just posterior to the triangular space, the branches to the long and lateral heads of triceps will be running separately along the surface of the tumour and similarly the branch to medial triceps leaves the main radial nerve just 2-3 cm distal to this point and lies on the surface of the nerve with the posterior cutaneous nerve of the arm fascicle group.
    It is essential that the operator understands the normal branching anatomy of nerves when exposing them for tumour removal.

    The loose connective tissue around the tumour has been mobilised and the tumour can be assessed more readily. The tumour is firm in consistency, however there are cystic areas which suggest that there has been some necrosis. Usually necrosis is followed by some degree of intramural scar which makes inter-fascicular dissection more challenging.

    Sloops are then placed around the proximal nerve above the tumourThe tumour has been mobilised and its cystic nature can be seen. The proximal neck of the tumour needs better visualisation to allow optimal siting of the epieneural window to expose the tumour. Typically the proximal and distal interface with normal nerve is the most challenging place to dissect and adjacent fascicles are at risk of injury at these points.
    I would recommend further dissection and an extended exposure plus if possible placing another sloop around the neck of the tumour. The proximal blue sloops have been placed around the long head of triceps motor branch (LHTBr) and the proximal radial nerve (PRN).
    More proximal dissection can be facilitated by releasing the lower border of teres major.

    There is a nerve fascicle lying on the surface of the tumour postero-medially.
    The nerve stimulator is being used to confirm that this is the motor branch origin for the medial head of triceps. This branch must be mobilised from the tumour and protected prior to evaluating where the epieneural window will be created to afford access to the tumour.

    The nerve is being inspected to assess where the fascicles lie in relation to the tumour. This step is essential to create the least traumatic cleavage plane between intact fascicles and the tumour.The medial triceps branch has been fully mobilised around the medial side of the tumour.
    The radial nerve fascicles (RNF) are identified in the upper lateral photograph adjacent to the more posteromedially positioned tumour. This is the cleavage plane and a longitudinal epineurotomy is made medial to the fascicles using the operating microscope.
    The tumour appears to have a significant vascular component which may represent an arteriorvenobs malformation or a site of intra neural vascular injury from the biopsy.
    The tumour should be carefully dissected tree from the main radial nerve trunk fascicles with attention to meticulous haemostasis of any feeding vessels using a combination of bipolar diathermy, ligament clips and suture ties.

    Once the location of the fasicles is appreciatedthe cleavage plane can be planned and a longitudinal epineurotomy is made using the operating microscope. The radial nerve is tagged with sloops proximally and distally around the radial nerve. The tumour can be easily seen in this nerve. It also appears to have a vascular component that is fluctuant with a palpable “thrill”.

    The tumour is dissected off the intact fascicles of the radial nerveThe plane is developed and the fascicles are protected in the blue sloop in the upper and lateral part of the photograph.
    The proximal “apex” of the tumour has been reflected inferiorly and the fascicles are gently peeled away from the tumour with intra-fascicular dissection. The fascicles and tumour are intimately related and the inferior tumour interface with normal fascicles is another site where fascicles may cross the dissection plane. The epineural window must be of sufficient length to fully evaluate the anatomy here before proceeding. The medial triceps branch can be seen deep to the radial nerve and tumour dissection where it was mobilised at the start of the nerve dissection.
    RN – radial nerve
    NT – nerve tumour
    MTB – medial triceps branch

    Great care should be taken when dissecting the distal tumour neck from the distal nerve stump in case there are crossing fascicles that could be injured.
    The epineurotomy should be of sufficient length to allow the fascicles to be seen and retracted from the tumour intra-neurally.

    The tumour has been removed. This dissection is an excision biopsy and usually results in a marginal excision. This is fine for a benign tumour in a critical mixed motor-sensory nerve. In cases of malignancy a wide excision or the compartment is recommended, with or without nerve reconstruction dependent on the bed, the type or nerve, the site of excision and the need for any adjunctive treatments.
    The management of malignant peripheral nerve sheath tumours is demonstrated in other techniques on the OrthOracle platform.

    Operation – 2

    Nerve stimulation is completed proximally on the radial nerve to ensure that there remains conduction, with preservation of some limited motor function distally.
    If there is a conduction block due to the dissection then stimulation proximally may be absent and no further conclusions can be made. Stimulation proximally with preservation is reassuring. Distal stimulation is unreliable because if there has been axonal disruption from dissection, the distal stimulation will still be apparent intra-operatively because Wallerian degeneration will not have yet run its course to full distal axon stump involution.
    In this case there was good contraction on stimulation of the triceps branches but only weak wrist and digit extension on stimulation with higher stimulation thresholds of 5.0mA.
    This poor stimulation may be interpreted as demonstrating poor axon recruitment due to axon damage (axonopathy).

    Here the exposure proximally allows visualisation of the radial nerve as it leaves the posterior axillary wall, traverses the triangular space beneath and distal to the teres major tendon and enters the posterior arm deep to the triceps lateral and long heads. The nerve stimulator is confirming retained function in the long head of triceps branch in the proximal medial exposure.
    No fascicles have been sacrificed with tumour excision and therefore no sural nerve harvest was required.

    The triceps interval is allowed to close and haemostasis is obtained prior to wound closure.The orientation has changed again and the photograph is taken from the posterior aspect of the patient with the shoulder in the lower part of the image and the elbow at the upper aspect of the image.

    The fascia is closed with a continuous absorbable suture (2’0 vicryl) and the subcutaneous fat and dermis is opposed in a similar way with 3’0 vicryl.

    A nerve catheter is sited under direct vision in the proximal aspect of the operative exposure with the tip adjacent to the radial nerve. The catheter is delivered through skin separate to the surgical incision using the supplied needle. the nerve catheter is useful for evaluating function post-operatively and then administering a boils of deep local anaesthetic next to the nerve to reduce the severity of post-operative neuropathic pain from nerve handling and dissection. A background infusion can be used to prevent blockage of the catheter with intermittent bolus infusions of local anaesthetic for break through pain with a long-acting agent.
    This is the author’s preferred technique and it reduced the opiate demand for the patient, especially in patients with pre-operative opiate requirements due to neuropathic pain from the tumour.

    The skin is closed with an absorbable, monofilament continuous suture (3’0 monacril) and supported with steristrips.

    The completed wound closure prior to application of steristrips and a waterproof adhesive dressing. The nerve catheter is seen in the proximal skin. `the nerve catheter does not require suturing in place. It will be removed after 48 hours if there is no significant neuropathic pain.

    Post Operative

    Occlusive dressings are applied and the patient has the operated arm placed in a poly-sling for support. A local anaesthetic infusion and intermitted boluses can be used for post-operative pain management. The nerve catheter can be removed after 48 hours. The dressing can be changed at this stage.
    After two weeks the dressing and steristrips are removed and the patient can allow the area to get wet. Scar massage is advised to help reduce sensitivity and ensure scar remodelling. The arm can be mobilised as soon as the patient is comfortable, typically within 5-7 days from surgery.
    Strengthening of the preserved radial nerve innervated muscles may be useful and if there is weakness this may be due to a conduction block from nerve dissection and handling. This should settle spontaneously within 3 months and should be monitored. Persistent weakness after 3 months may be related to axonal damage and electromyography of the radial nerve innervated muscles may demonstrate denervation changes may be useful to confirm axonopathy. Sensory conduction velocity recording in the superficial radial nerve may show reduced amplitude in axonopathy.
    A functional motor loss persisting beyond three months and not showing progressive recovery, can be considered for high radial tendon transfer reconstruction. Nerve transfers at the forearm level are an alternative method of reconstruction, however the onset of motor loss is unclear due to the longstanding nature of the tumour and the uncertainty regarding the cause of the deterioration following the biopsy. Tendon transfers are more reliable than nerve transfers in such cases.

    Recommended Reading

    References:
    The published literature reports good resolution of pre-operative neurological symptoms with surgical excision of benign peripheral nerve sheath tumours. Unfortunately, new neurological sensory and motor deficits do occur following biopsy or surgery but many resolve spontaneously or are not at a level that causes functional impairments. The rates of new permanent motor deficits after surgery are variable with typical rates quoted between 5 and 17%. In the largest published series by Desai in 2017 the rate of new motor deficit was 6.3% with 2 of 442 tumours showing regrowth or recurrence. There is some evidence to suggest that larger tumours have a higher rate of post-operative neurological deficit.
    Bendon CL, Furniss D, Giele HP. Comparison of outcomes of peripheral nerve schwannoma excision in neurofibromatosis type 2 patients and non-neurofibromatosis type 2 patients: A case control study. J Last Reconstr Aesth Surg. 2015 Sep;68(9):1199-203
    Hooper J, O’Connor IT, Golub IJ, Decilveo AP, Wittig JC. Retrospective Analysis of 20 Patients With Schwannomas: Magnetic Resonance Imaging Characteristics, Pain, and Outcomes Following Excision. Orthopaedics. 2017 Nov 1;40(6):e1036-e1043
    Desai KI. The Surgical Management of Symptomatic Benign Peripheral Nerve Sheath Tumors of the Neck and Extremities: An Experience of 442 Cases. Neurosurgery. 2017 Oct 1;81(4):568-580
    Gosk J, Gutkowska O, Urban M, Wnukiewicz W, Reichert P, Ziolkowski P. Results of surgical treatment of schwannomas arising from extremities. Biomed Res Int. 2015:547926
    Kim SM, Seo SW, Lee JY, Sung KS. Surgical outcome of schwannomas arising from major peripheral nerves in the lower limb. Int Ortho. 2012 Aug;36(8):1721-5

    Reference

    • orthoracle.com

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